Method to print organic electronics without changing its properties

ABSTRACT

Method for high throughput, highly reproducible, direct write plasma jet deposition of organic electronic materials through nozzles containing non-concentric tubes with inner tube having higher dielectric constant and/or higher wall thickness than the outer tube, so that the inner tube containing the aerosol of organic electronic materials is shielded from the outer tube containing plasma and the organic electronics is focused at the outlet of the nozzle through the after-glow region of the atmospheric pressure plasma. Ensuring reproducibility of the method for printing organic electronic materials by removing the contaminants and residues in inner tube using reactive gas and generating a plasma discharge at a potential significantly higher than the operating potential for printing so that the plasma is generated in both the inner and outer tube for dielectric barrier discharge plasma jet based cleaning of the nozzle.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to the high throughput direct write printing ofconducting electronic materials, using the after-glow region of theatmospheric pressure dielectric barrier discharge plasma jet, withoutchanging the material properties and chemical structure upon printing.

Description of the Background

With the development of organic electronic materials, there is a needfor developing high throughput printing technology to meet the growingneeds for fabrication of organic light emitting diodes, organicphotovoltaics, electronic papers, wearable electronics, touch panels,flexible displays and sensors.

Deposition of organic conducting polymers, small molecules, dendrimers,fluorescent and phosphorescent molecules in a high throughput fashion ischallenging as it is absolutely essential to retain the chemicalstructure and bonding environment of the materials upon printing.

Any change in the chemical bonding and or chemical structure will resultin poor performance behavior with deteriorated conductingcharacteristics.

In a display device using organic light emitting diodes, several layersof materials will be printed including anode, cathode, hole injectionlayer, emissive layer, interlayer etc., which is required for improveddevice performance. Different layers require materials with varyingcharacteristics including transparent conducting oxides which requireboth good optical properties as well as conducting properties.

Deposition of materials with dual functionalities like good opticalbehavior as well as good electronic conduction behavior require printingmethods that will enable printing inks in a highly directional and highthroughput fashion without compromising the optical and electronicproperties.

Currently a combination of one or more techniques including vacuumevaporation, vacuum based plasma sputtering, screen printing,photolithograpy, ink jet printing, aerosol printing etc., are used toprepare display screens, photovoltaic devices, flexible electronicdevices etc.

Photolithography, screen printing, laser induced sintering, plasmaspray, inkjet printing, aerosol printing, laser sintering are allexplored for site selective printing of metals and metal oxides, andorganic electronics.

Different deposition tools and methods must be adopted for differentmaterials depending on the nature and type of substrate, material to bedeposited and the substrate area. This also means increased processingtime and increased number of printing tools required for differentmaterials.

Atmospheric pressure plasma based printing of electronic materials havebeen reported. However, the method described in the literatures willchange the properties of the materials as the aerosol containingelectronic materials enters the plasma region due to the presence ofhigh energy ions, radicals and electrons in the plasma region. Theeffect of plasma on the chemical structure of materials resulting inpolymerization is a known phenomenon. There is a need to shield theelectronic materials from direct exposure to high energy plasmadischarge region between the electrodes.

SUMMARY OF THE INVENTION

Fabrication of devices that use organic electronics, including displaydevices, photovoltaic devices, touch displays, optoelectronic devices,flexible electronics and wearable electronics, needs high throughputdeposition methods that can deposit organic electronics and associatedelectronic materials in a controlled fashion without compromising thefilm quality and device performance.

Vacuum evaporation techniques, vacuum plasma sputtering methods, inkjetprinting, screen printing, aerosol printing are the techniques widelyused for fabrication of display devices and flexible electronic devices.

The organic light emitting diode (OLED) display devices, touch panels,flexible displays and photovoltaic devices require multiple layers ofmaterials including cathode coating, anode coating, electron injectionlayer, electron transporting layer, exciton/hole blocking layer,emissive layer, exciton/electron blocking layer, hole transportinglayer, hole injection layer and interlayers that exhibit varying opticaland electronic properties

Transparent conductive oxides (TCO) are used as transparent electrodematerials in optoelectronic devices, touch panels, flat displays,organic photovoltaics, organic light emissive devices, etc. Theseelectrode materials are prepared using vacuum evaporation, vacuum (lowpressure) plasma sputtering, chemical vapor deposition,electro/electroless chemistry etc.

Deposition of additional organic electronic materials andelectroluminescent materials requires methods other than those used fortransparent conductive oxide film fabrication, as the organic materialsperformance depends strongly on the method of preparation.

Deposition of small molecules, conjugated polymers, electro luminescentlayers, conducting polymer layers etc., requires printing techniquesthat will not alter the chemistry and bond structure of the conductingpolymer and electro luminescent/light emissive layers.

Screen printing and ink jet printing methods require pre- andpost-processing to enhance the adhesion and to optimize the performanceof device. Also, these techniques require substrates to be placedparallel to the ground as the ink dispensing is designed to work onsurfaces placed parallel to the ground rather than upright position orfacing the wall.

Plasma jet printing techniques described in the prior art for printingof electronic materials will not work for organic electronics, smallmolecules, conjugated polymers and electroluminescent materials, as theintense plasma region between the positive and ground electrode isintense and rich in electrons, ions and free radicals for all types ofgases used for creating the discharge.

The plasma species in the plasma region between the electrodes caneither polymerize the organic materials or break the conjugated bondswhich are crucial for electronic conductivity and optimal deviceperformance. However, the plasma jet could be effectively used fordirecting the organic electronic materials and for increasing thethroughput of the printing.

This invention discloses high throughput plasma jet printing of organicelectronic materials, small molecules, conjugated polymers,electroluminescent materials and other electron, hole injection,emissive layers without changing its material properties during plasmaprinting.

Atmospheric pressure plasma jet with dielectric barrier discharge isused for this purpose. However, the nozzle is designed in such a waythat only the after-glow region of the atmospheric plasma, which doesnot contain energetic plasma species, comes in contact with the aerosolcontaining organic electronic materials, and the plasma regioncontaining the high energy plasma species is shielded from directinteraction with the aerosol containing organic electronic materials.

This method uses after-glow of the plasma discharge to propel thematerial towards substrate while preventing the aerosol containingorganic electronic materials from getting directly exposed to the plasmazone between the electrodes.

The printing nozzle consists of two non-concentric tubes with the outertube containing the electrodes connected to high voltage power supply,and the inner tube that carries the aerosol of organic electronicmaterials to the substrate.

The outer tube connected to a gas source will contain a plasmadischarge.

The inner tube is made of higher dielectric constant or thicker innerwall than the outer tube so that the plasma is contained only in outertube and shielded from high energy species of the plasma in the innertube.

The nozzle contains two regions i) plasma region that exists inside theouter tube (in between the outer wall of the inner tube and inner wallof the outer tube) and in between the two electrodes placed at theoutside tube and ii) after-glow region that extends beyond the nozzleoutlet.

The plasma region contains high energy plasma species includingaccelerating electrons, ion, free radicals and excited species whichwill affect the material properties of the organic electronic materialsif the material comes in contact with the plasma species in plasmaregion. The after-glow region contains de exciting plasma species withmuch less electron density, ion density, electron temperature, iontemperature and much less free radicals which will not affect thematerial properties if carefully controlled.

The plasma jet printing nozzle design of the invention contains bothplasma jet and an aerosol of organic electronic material separated by adielectric material that protects organic electronic materials in theaerosol from getting directly exposed to high energy plasma species.

The nozzle head of the preferred embodiment of the invention consists oftwo non-concentric tubes to enable directionality and to get anincreased after-glow region immediately outside the nozzle so that theafter-glow plasma discharge is efficiently used for printing organicelectronic materials that is carried through an aerosol and a gasthrough the inner tube of the nozzle.

Unlike the plasma jet printing techniques of the prior art, thistechnique prevents aerosol containing organic electronic materials fromgetting directly exposed to the high energy plasma species in the plasmaregion which could potentially change the chemical structure of theorganics.

Therefore, there is presented according to the invention, systems andmethods for focused plasma jet deposition of organic electronicmaterials without changing its material properties by the plasma speciesby containing aerosol through non-concentric nozzles connected to highvoltage power supply, in the presence of electric field and plasma, thatenables printing of organic electronic materials in the aerosol usingthe after-glow region of the atmospheric pressure dielectric barrierdischarge plasma.

The outer non-concentric nozzle that sustains the plasma and throughwhich the gas for creating the plasma discharge is fed is connected tohigh voltage power supply through one or more electrodes. The nozzle canbe made of any or all of the following silicon wafer, quartz, glass,ceramic, plastic, machinable ceramic, glass reinforced epoxy, polyimide,polyetheretherketone, fluoropolymer, aluminum, silicon wafer containinglayers of silicon oxide and metals layers embedded on it.

The diameter of the nozzle used for deposition of conducting metallayers can be varied from about 10 mn to about 50 mm. The diameterdetermines throughput, deposition rate, pattern size, etc.

The electrodes connected to the nozzle to create the plasma can eitherbe externally bound or patterned and deposited to be part of the nozzleby using silicon micro machining and micro electromechanical systemsprocessing depending on the diameter requirement of the nozzle and theresolution of the metal deposition needed.

In the case of a silicon micro machined nozzle, the nozzle on thesilicon substrate can either be formed using any of the known siliconprocessing steps like wet etching, dry etching, deep reactive ionetching.

Non concentric type nozzles can be created by wet chemical etching ofsilicon substrates.

The nozzle can be connected to a range of reactive and or non-reactivegases depending on the requirements.

The organic electronic materials in the aerosol upon entering theafter-glow region just outside the nozzle is carried forward to thesubstrate by less energetic deexciting plasma species.

The electronic materials to be printed using the after-glow region ofthe plasma jet printer could include any of the following materialsconjugated polymer, poly[9,9-dioctyl fluorine-co-N-(4-butylphenyl)diphenylamine] (TFB), poly(3,4-ethylenedioxythiophene) and poly(styrenesulfonic acid) (PEDT: PSS, hole injection layer), emissive polymerpoly(9,9-dioctyl fluorine-co-benzothiadiazole) (F8BT), small molecule,fluorescent phosphorescent materials, dendrimers, poly phenylene, polyfluorene, poly phenylene, dithienyl benzothiadiazole, poly fluorene,poly carbazole, poly vinyl carbazole, transparent conducting oxidesincluding indium oxide, zinc oxide, tin oxide nanomaterials, carbonnanotubes, nickel oxide, aluminum oxide, copper oxide, copper aluminumoxide, indium based oxides, zinc based oxides, indium tin oxide, silver,silver oxide,N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-diphenyl-4,4′-diamin (TPD),tris-(8-hydroxyquinoline) aluminum (Alq₃).

In order to get reproducible coating over a large cycle, it is essentialto clean the inner tube to remove the contaminants and residues so thatthe printed organic electronic materials retain the required propertiesand are not altered during deposition.

The reproducibility of organic materials printing can be achieved byusing a plasma cleaning step by allowing reactive gases inside the innertube and igniting a plasma discharge at a potential significantly higherthan the operating potential for printing so that the plasma isgenerated both in the inner tube and outer tube. This will enablecleaning of residues formed during deposition and ensure reproducibledeposition

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of the plasma jet printer nozzle according toan embodiment of the invention containing non-concentric tubes withinner tube having a higher dielectric constant or wall thickness higherthan the outer tube and with the outer tube having a conical shaped wallfocused towards the nozzle outlet such that the gas in the outer tubeundergoes turbulence and creates high pressure at the nozzle that drivesthe gas with high pressure and increased after-glow region.

FIG. 2 shows a schematic of the plasma jet printer nozzle according toan embodiment of the invention containing two non-concentric tubes withthe inner tube inclined at an angle above 0.1 degree and up to 45degrees with provisions for the addition of various process gasesthrough the sides of the outer nozzle. Various process gases includinghelium, argon, hydrogen, nitrogen, carbon dioxide, oxygen, methane,alkane, alkene, silane, carbon tetra fluoride, sulfur hexafluoride,etc., can be used on their own or with appropriate mixture to suitvarious requirements.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the schematic of the plasma jet printer nozzle for highthroughput direct write printing of organic electronic materials usingthe after-glow region of the atmospheric pressure plasma and shieldingof the aerosol containing organic electronics from the high energyplasma species generated in the dielectric barrier discharge. Variousprocess gases including helium, argon, hydrogen, nitrogen, carbondioxide, oxygen, methane, alkane, alkene, silane, carbon tetra fluoride,sulfur hexafluoride, etc., can be used on their own or with appropriatemixture to suit the need and depending on the suspension of the organicelectronic material.

FIG. 1 shows the following elements:

-   -   Non concentric conical shaped outer tube 1 with a specific        dielectric constant and a specific wall thickness, with a narrow        end at the outlet of the nozzle;    -   Inner tube 2 with a dielectric constant and/or wall thickness        higher than that of tube one;    -   Inner region 3 of the inner tube where the aerosol containing        organic electronic materials will be transported towards the        substrate by a feed gas and also the region that will be        shielded from plasma in the outer region by the inner tube;    -   Plasma region 4 of the outer tube where a gas for creating        discharge is fed and undergo high pressure constriction at the        narrow region, and also the region rich in high energy plasma        species including electrons, ions, free radicals, excited        species, metastable species with high electron and ion density;        this region corresponds to the area inside the outer tube and        between the electrodes;    -   After glow region 5 outside the nozzle where the electrons and        ions are at very low energy and contain mainly deexcited        species, with low electron and ion density than the plasma        region 4 existing between the electrodes 6 in outer tube;    -   Electrodes 6 placed in the outer side of the outer tube and        connected to the high voltage power supply for generating plasma        in the region 4;    -   Inlet 7 for gas that generates a plasma discharge in the region        4 and an after glow in the region 5;    -   Inlet 8 for aerosol containing the organic electronic materials        and other electronic materials to be printed. This is also the        inlet for passing reactive gases for plasma cleaning of the        inner nozzle to retain the reproducibility of the printing        process.

FIG. 2 shows the following elements:

-   -   Non concentric conical shaped outer tube 1 with a specific        dielectric constant and a specific wall thickness, with a narrow        end at the outlet of the nozzle;    -   Inner tube 2 with a dielectric constant and/or wall thickness        higher than that of tube one;    -   Inner region 3 of the inner tube where the aerosol containing        organic electronic materials will be transported towards the        substrate by a feed gas and also the region that will be        shielded from plasma in the outer region by the inner tube;    -   Plasma region 4 of the outer tube where a gas for creating        discharge is fed and undergo high pressure constriction at the        narrow region, and also the region rich in high energy plasma        species including electrons, ions, free radicals, excited        species, metastable species with high electron and ion density;        this region corresponds to the area inside the outer tube and        between the electrodes;    -   After glow region 5 outside the nozzle where the electrons and        ions are at very low energy and contain mainly deexcited        species, with low electron and ion density than the plasma        region 4 existing between the electrodes 6 in outer tube;    -   Electrodes 6 placed in the outer side of the outer tube and        connected to the high voltage power supply for generating plasma        in the region 4;    -   Inlet 7 for gas that generates a plasma discharge in the region        4 and an after glow in the region 5;    -   Inlet 8 for aerosol containing the organic electronic materials        and other electronic materials to be printed; this is also the        inlet for passing reactive gases for plasma cleaning of the        inner nozzle to retain the reproducibility of the printing        process; the axis of the outer tube being 9;    -   The axis of the inner tube in 10 and different from 9 with angle        between 0.1 degree to 45 degrees;    -   organic electronic materials 11 being directed by the after-glow        region 5 on to the substrate 12;

According to one embodiment of the invention; the plasma jet printernozzle preferably consists of non-concentric outer and inner tubes 1 and2 made of any one or more of the following: silicon, silicon wafer,quartz, glass, ceramic, plastic, machinable ceramic, glass reinforcedepoxy, polyimide, polyetheretherketone, fluoropolymer, aluminum, or anyother dielectric material. The outer tube also may contain two metalelectrodes 6 connected to high voltage power supply for creating aplasma discharge in the plasma jet chamber. The high voltage powersupply can be any one of the following AC, DC, radio frequency, pulsedpower supply. The after-glow region 5, through which the material to bedeposited is focused to the substrate.

The outer and inner tubes 1 and 2 can either be made of same dielectricmaterials but with different wall thickness, with 2 preferably beingthicker than 1, or the outer and inner tubes can be made of twodifferent materials with varying dielectric constant with inner tube 2having a higher dielectric constant than the outer tube 1.

Nonreactive, noble gases like helium, argon etc., can be used to createthe discharge as well as for printing. In order to retain the chemicalcharacteristics, electronic properties and optical properties of thematerials, any of the non reactive gases including helium, argon,nitrogen could be used or gases which are compatible and non reactivewith the solution of the organic electronic material. Reactive gasesincluding nitrogen, oxygen, hydrogen, carbon dioxide, alkane, alkene,carbon tetra fluoride, sulfur hexafluoride etc., can be used forcleaning of the nozzle. The reactive and non-reactive gases can eitherbe used on their own or with appropriate mixture of gases to obtain therequired plasma processing condition.

The material to be coated may either taken as a colloid or as a solutionand the colloid/solution is aerosolized and carried by a carrier gasinto the non-concentric plasma jet tube where a plasma discharge isgenerated in the outer region 4 and the aerosol in region 3 is shieldedfrom the high energy plasma species by the dielectric 2. Depending onthe nature and type of nanomaterial/micromaterial/solution used, natureand type of coating required, concentration of the material incolloid/solution, and the nature and type of substrate used, the plasmaprocess parameters may be tailored using appropriate gas mixtures, gasflow ratios and electrical energy input for generating the plasma.

In order to get an after-glow region that stays outside the nozzle andhelp print the organic electronic materials without changing itsmaterial properties, appropriate mixture of gases, gas flow ratios,concentration and electrical energy input are optimized to obtaindesired film characteristics.

The electronic properties, optical properties, electro luminescentproperties of the printed material will be maintained and optimized byappropriate choice of gas mixture and plasma process parameters.

Among the significant advantages of the present invention is the abilityto print organic electronic materials in a high throughput fashion usingthe after-glow region of the atmospheric pressure plasma discharge andshielding the aerosol containing organic electronics from the highenergy species of the plasma region between the electrodes using higherdielectric constant inner tube or inner tube with thicker wall toprevent plasma species surrounding the inner tube from interacting withthe aerosol.

Display devices, touch panels, organic light emitting diodes,photovoltaic devices and similar such devices that use organicelectronic materials required to be printed using multiple techniqueswith pre and/or post processing and longer processing time can now beaccomplished with direct write plasma jet printing of the presentinvention. The after-glow-based direct write plasma jet printing allowschemical structure, electronic properties and optical properties to bemaintained and preserved during the printing process by appropriatechoice of gas and plasma process parameters.

The electron density of the plasma depends on various processconditions, and one prominent feature deciding the electron density ofthe plasma is the nature of gas used to generate the discharge. Theelectron densities in argon and helium are different. Argon plasma hashigher electron density than the helium plasma for the same processparameters and for atmospheric pressure plasmas the electron density inargon is 2.5 times higher than helium. The thermal conductivity of gasesalso varies. As a result, the energy of the plasma varies depending onthe nature and type of gases used to generate the discharge. When theaerosol containing organic electronic material enters the plasma, itwill be subjected to electrons, ions and radical bombardment from theplasma species resulting in serious chemical structure change andmodification of electronic and optical properties which will deterioratethe device performance. In order to avoid this the inner tune of thenozzle is designed in such a way that the plasma generated by dielectricbarrier discharge will only be present in the outer tube and the innertube will remain inert to the plasma species. The aerosol containing theorganic electronic materials will only interact with the after-glowregion of the plasma present outside the nozzle which will have muchlesser ion and electron density as well as less energetic deexcitingspecies that will not alter the material properties if properlycontrolled.

Having now fully set forth the preferred embodiments and certainmodifications of the concept underlying the present invention, variousother embodiments as well as certain variations and modifications of theembodiments herein shown and described will obviously occur to thoseskilled in the art upon becoming familiar with said underlying concept.It should be understood, therefore, that the invention may be practicedotherwise than as specifically set forth herein.

The invention claimed is:
 1. A plasma jet printer for high throughputdirect write printing of conducting electronic materials comprising: twonon-concentric tubes, with an inner tube located inside an outer tube;said inner tube having at a first end an inlet through which an aerosolof electronic materials is introduced, said outer tube having a gasinlet through which a gas is introduced, an electrode assembly on theouter tube connected to a high voltage power supply for creating aplasma from said gas between the inner tube and the outer tube; anebulizer connected to the inlet at the first end of the inner tube forgenerating the aerosol of electronic materials; said inner tube having asecond end through which said aerosol of electronic materials exits;said outer tube having discharge end through which said plasma isdischarged; said second end of said inner tube and said discharge end ofsaid outer tube located in a common plane; and a substrate placedadjacent said second end of said inner tube and said discharge end ofsaid outer tube to receive said discharged plasma and aerosol ofelectronic materials.
 2. The plasma jet printer according to claim 1,wherein the aerosol of electronic materials can be organics, metalsand/or metal oxides.
 3. The plasma jet printer according to claim 1,wherein the aerosol of electronic materials includes poly[9,9-dioctylfluorine-co-N-(4-butylphenyl) diphenylamine] (TFB),poly(3,4-ethylenedioxythiophene) and poly(styrene sulfonic acid) (PEDT:PSS, hole injection layer), emissive polymer poly(9,9-dioctylfluorine-co-benzothiadiazole) (F8BT), small molecule, fluorescentphosphorescent materials, dendrimers, poly phenylene, poly fluorene,poly phenylene, dithienyl benzothiadiazole, poly fluorene, polycarbazole, poly vinyl carbazole, transparent conducting oxides includingindium oxide, zinc oxide, tin oxide nanomaterials, carbon nanotubes,nickel oxide, aluminum oxide, copper oxide, copper aluminum oxide,indium based oxides, zinc based oxides, indium tin oxide, silver, silveroxide, N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-diphenyl-4,4′-di-amin(TPD), tris-(8-hydroxyquinoline) aluminum.
 4. The plasma jet printeraccording to claim 1, where the gas includes non-reactive noble gaseslike argon, helium.
 5. The plasma jet printer according to claim 1,wherein various process gases including helium, argon, hydrogen,nitrogen, carbon dioxide, oxygen, methane, alkane, alkene, silane,carbon tetra fluoride, sulfur hexafluoride, etc., can be used on theirown or with appropriate mixture to suit various requirements.